Method and apparatus for purifying untreated water

ABSTRACT

The invention relates to the purification of untreated water which is polluted with dissolved organic carbon compounds which can be biologically or adsorptively removed in a three-step process, whereby the upstream purification step is predominantly biological, i.e. operates as a biofilter ( 1 ), and both subsequent purification steps are predominantly adsorptive in nature, i.e. operate as adsorbers ( 2, 3 ). The biofilter ( 1 ) is purified by backwashing, whereby the backwashing periods occur according to the TOC determined between the biofilter ( 1 ) and the upstream adsorber ( 2 ) and/or running time and/or pressure loss. The upstream adsorber ( 2 ) is also cleaned by backwashing and is subsequently shifted into a downstream position alternating with the other adsorber ( 3 ). The method is suitable for obtaining TOC concentrations in treated water of less than 500 ppb.

BACKGROUND OF THE INVENTION

The invention relates to a method as well as an apparatus for thepurification of untreated water that is polluted with substances,especially dissolved organic carbon compounds, that can be biologicallyand adsorptively removed, especially for the preliminary purification ofchlorine-free drinking water as a preliminary step for the production ofhigh-purity water from which minerals and salts have been completelyremoved.

SUMMARY OF THE INVENTION

It is an object of the invention to enable a particularly effective andhence particularly economical purification of the untreated water.

To accomplish this, the invention proposes,

-   -   that the purification is carried out in three stages,    -   that the upstream purification stage is operated predominantly        biologically as a biofilter, and the subsequent purification        stages are operated predominantly adsorptively as adsorbers,    -   that the biofilter is cleaned by backwashing, whereby the        backwash periods are initiated as a function of the TOC        determined between the biofilter and the upstream adsorber        and/or as a function of the running time and/or as a function of        the pressure loss over the biofilter, and    -   that the upstream adsorber is cleaned by backwashing and is then        shifted to the downstream position by alternating it with the        other adsorber.

Biofilters for the purification of untreated water, for example for theproduction of drinking water, are known. It is also known to useadsorbers for the water purification. In both cases one operates withactivated carbon, as is also preferably the case with the presentinvention. The effectiveness of the known methods is, however, limited.In addition, the activated carbon must frequently be exchanged,resulting in a considerable cost burden. Also known is the use ofmicrofilters, whereby these filters allow a very high degree ofeffectiveness to be achieved. They are even suitable for producing ultrapure water, as is required for the manufacture of chips. However, thecosts for carrying out a microfiltration are extremely high.

The inventively proposed 3-stage method is in a position to achieve ahigh degree of effectiveness at a relatively low cost. The method servesprimarily as a preliminary stage for the production of high-purity waterfor industrial use. Involved is a closed process with which only easilyusable residues result. The method is suitable for achieving TOCconcentrations in processed water of <500 ppb.

The untreated water is conditioned in such a way that in the biofilter ahigh biological activity is achieved that is enhanced by an extensivelyconstant hydraulic charge. The biofilter is monitored by determining theTOC (TOC stands for Total Organic Carbon) in the filtrate. As soon asthe TOC has risen to a prescribed value, a backwashing of the biofilteris effected. A break-through of TOC to the upstream adsorber can thus beeffectively prevented. There is also no blockage of the biofilter. Thebackwashing reduces the solid content/biomass to the respective minimumquantities that are required for the reliable functioning of thebiofilter. The activated carbon of the biofilter does not need to beexchanged. In addition, or alternatively to the TOC monitoring, thebackwashing of the biofilter can also be initiated as a function of therunning time (determined by the throughput) or as a function of thepressure loss over the biofilter.

The subsequent, upstream adsorber is also backwashed, and is therebyprotected against premature depletion. It serves to receive and toadsorb the slippage of TOC and impurities that occurs in the biofilter.The upstream adsorber has only a very slight biological function. Itseffectiveness is predominantly an adsorption function to reduce theadsorptively removable TOC. As a consequence of the backwashing, theactivated carbon is kept in a mechanically clean state and remainseffective for a long period of time, so that an exchange is requiredonly at very great time intervals. This contributes considerably to theeconomy of the inventive method.

The downstream adsorber enables not only an optimization of thepurification process, but rather also permits a nearly constant andcontinuous maintenance of a very high effectiveness. In particular, ifthe upstream adsorber is cleaned, the downstream adsorber takes over itsfunction. It thus becomes the upstream adsorber, where upon the freshlycleaned adsorber assumes the downstream position, and now in turnoptimizes the purification process. The shift or alternation enables ahigh and constant adsorption efficiency and the utilization of the fulladsorption capacity of both of the adsorbers.

A preferred application of the invention is the pre-purification duringthe production of high-purity water from which salts and minerals arecompletely removed, as it is used, for example, as process water inindustrial processing engineering and the chemical industry, or also asfeed water for boiler plants. Following the purification is a salt ormineral removal stage that operates as reverse osmosis or ion exchange.

An important recognition that lies at the basis of the invention is thatafter the removal of chlorine, the growth of micro organisms increasessuddenly due to the increased substrate content. Without the effectivereduction of substrate concentration made possible by the invention,there would thus result an impermissible contamination of the downstreamunit for removing salt and minerals due to germination and biofouling.In the biofilter, the substrate concentrations are mineralized and areconverted into the biomass or into other substances. These andnon-assimilated substances (TOC slippage) are adsorbed in the subsequentadsorbers.

By means of suitable conditioning measures, primarily by regulating thetemperature and the oxygen content, a high biological activity ismaintained in the biofilter. With a relatively long contact time, thereresults a reduction of the predominantly biologically removable TOC. Thesubsequent adsorbers reduce the adsorptively removable TOC.

The biofilter can be built up during the operation. More advantageous isto use an already seeded filter.

As a further development of the invention, it is proposed that thebackwashing of the biofilter be synchronized with the backwashing of theupstream adsorber. During the backwashing of the biofilter, the upstreamadsorber should be ready for use, so that in cooperation with thedownstream adsorber it can briefly help assume the function of thebiofilter. The time control is in this connection preferably such thatthe shifting of position of the two adsorbers has taken place shortlybefore the backwashing of the biofilter is carried out.

It can furthermore be advantageous to initiate the backwash periods ofthe upstream adsorber as a function of the TOC that is determinedbetween this adsorber and the downstream adsorber. The backwash periodsof the upstream adsorber, and possibly synchronously therewith thebackwash periods of the biofilter, can thus also be initiated as afunction of the loading of the upstream adsorber. This prevents anoverloading of the downstream adsorber.

The reliability of the purification process can additionally beincreased by additionally or alternatively initiating the backwashingperiods as a function of the pressure loss determined over the upstreamadsorber.

Each of the backwashing periods preferably includes a lowering of thewater level in the biofilter or in the upstream adsorber, and then abackwashing with air and/or with water. After the lowering of the waterlevel, it is particularly advantageous to first loosen the activatedcarbon with air, so that a subsequent backwashing with water results ina particularly high degree of effectiveness. This is of particularsignificance with regard to the time required for the backwashing.Finally, during the backwashing the three-stage purification process isreduced to a two-stage process.

Pursuant to a significant further development of the invention, it isproposed that during times that are free of a removal of water, thebiofilter be separated from the upstream adsorber, and the two adsorbersbe switched off.

Frequently, for example on weekends and holidays, there is no need tomake purified or pre-purified water available. In this connection, theunit cannot be switched off, since otherwise the biofilter would beadversely affected. However, if during the times that are free of waterremoval one would charge the adsorbers with the filtrate of thebiofilter, the inherently produced purified or pre-purified water wouldhave to be discarded. After switching off the adsorbers, it is merelynecessary to re-circulate the filtrate of the biofilter. It is ofparticular significance that during the times that are free of waterremoval the adsorbers in no way be charged by the filtrate of thebiofilter. This increases the time spans between the backwash periods ofthe upstream adsorber, and extends the service life of the activatedcarbon filling of the two adsorbers.

During the times that are free of the removal of water, the biofilter,which is separated from the upstream adsorber, is preferably operatedwith a reduced throughput, since this is sufficient for maintaining thebiological activities.

Thus, the invention makes it possible to avoid the TOC slippage throughthe entire unit. The danger of a bacterial contamination of downstreamcomponents of the unit is greatly reduced. The same applies for theblockage of functional groups of the ion exchange resin of the unit forthe complete removal of salt and minerals. The operating costs arereduced, and only easily usable residues are produced.

The invention furthermore provides an apparatus for carrying out thepreviously described method, namely for the purification of untreatedwater that is polluted with substances, especially dissolved organiccarbon compounds, that can be biologically and adsorptively removed,especially for the preliminary purification of drinking water from whichchlorine has been removed as a preliminary step for the production ofhigh-purity water from which minerals and salts have been completelyremoved, whereby this apparatus has the following features:

-   -   a feed line for untreated water,    -   a drain line for purified water,    -   a biofilter, the inlet of which is connected to the feed line        for untreated water,    -   a first and a second adsorber, the inlets of which are        connectable to the feed line for untreated water and to the        outlet of the biofilter, and the outlets of which are        connectable to the drain line for purified water, whereby        furthermore the outlet of the first adsorber is connectable to        the inlet of the second adsorber and the outlet of the second        adsorber is connectable to the inlet of the first adsorber,    -   a feed line as well as a drain line for backwash water and/or a        feed line for backwash air, whereby the lines are connectable to        the biofilter as well as to each of the two adsorbers, and    -   a control device for the operation of the valves that are        associated with the biofilter and each of the two adsorbers,        whereby the control device is connected with a TOC measurement        location on the outlet of the biofilter and/or with a throughput        measurement device and/or with a differential pressure        measurement device for the biofilter.

Further preferred features are provided in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in greater detail subsequently with theaid of a preferred embodiment in conjunction with the accompanyingdrawing. The drawing shows in:

FIG. 1 a control diagram of an apparatus for the purification ofuntreated water.

DESCRIPTION OF PREFERRED EMBODIMENTS

Pursuant to FIG. 1, a biofilter 1 is provided which is followed inseries by two adsorbers, namely a first adsorber 2 and a second adsorber3. The inlet of the biofilter 1 is connected to a feed line 4 foruntreated water, whereby it is advantageous to introduce oxygen into theinlet in a controlled manner in order to avoid an under supply of oxygento the micro organisms. Furthermore, the outlet of the second adsorber 3is connected to a drain line 5 for purified water. The temperature ofthe feed of the biofilter is preferably monitored and regulated.

The diagram of FIG. 1 shows in heavy, solid lines one of the paths thatthe water can take from the feed line 4 for untreated water through thebiofilter 1 and the two adsorbers 2 and 3 to the drain line 5 forpurified water. In accordance therewith, the adsorber 2 operates as anupstream adsorber. It adsorbs a significant portion of the TOC thatoverflows out of the biofilter 1. Its biological activity is slight.Emphasized is its adsorption capacity.

The downstream adsorber 3 optimizes the purification process and, afterappropriate shifting, takes over the function of the upstream adsorber,while the first adsorber is backwashed and is then shifted to thedownstream position.

Provided at the outlet of the biofilter 1 is a TOC measurement location6. It is in communication with a non-illustrated control device thatoperates the plurality of valves that are associated with the unit. Assoon as the TOC measurement location 6 indicates a preselected value,the biofilter 1 is shifted to backwash.

The backwash system includes a feed line 7 and a drain line 8 forbackwash water, as well as a feed line 9 for backwash air.

The backwashing of the biofilter 1 is initiated by closing its inlet andits outlet. A line section 20 serves as a bypass and connects the inletof the first adsorber 2 with the feed line 4 for untreated water. Thewater level in the biofilter 1 is then lowered, and in particular via aline section 11 that connects its outlet with the drain line 8 forbackwash water. There is then effected a loosening of the activatedcarbon in the biofilter 1. For this purpose, the latter is connected viaa line section 12 to the feed line 9 for backwashed air. Venting can beeffected into the drain line 8 for backwash water. As the last step, thebiofilter 1 is connected via a line section 13 to the feed line 7 forbackwash water. As soon as the cleaning process is terminated, theoriginal operation is again undertaken.

As an additional safety measure, the biofilter 1 is provided with adifferential pressure measurement device 14 that is connected to thecontrol device and ensures that the backwashing of the biofilter 1 isstarted even if the pressure drop over the biofilter exceeds aprescribed maximum value.

The backwashing of the two adsorbers 2 and 3 is carried out in acorresponding manner. The components required to accomplish this thatcoincide with those of the biofilter 1 have reference numerals in thehundreds for the adsorber 2 and in the two hundreds for the adsorber 3.

The backwashing of the upstream adsorber, which according to the controldiagram illustrated in heavy, solid lines in FIG. 1 is the firstadsorber 2, can be effected synchronously with the backwashing of thebiofilter 1, although under the condition that the latter is inoperation. As a first step, the inlet of the adsorber 2 is closed,whereby at the same time the inlet of the adsorber 3 is connected to theoutlet of the biofilter 1, and in particular via a line section 15.

The adsorber 3 now takes over the entire adsorption capacity. After itsoutlet is closed, the adsorber 2 is backwashed in the same way as wasdescribed in conjunction with the biofilter 1.

After conclusion of the backwashing of the adsorber 2, it is connecteddownstream of the adsorber 3. The latter thus obtains its upstreamposition, while the adsorber 2 assumes the downstream position. For thispurpose, the connection between the outlet of the adsorber 3 and thedrain line 5 for purified water is interrupted. Instead, the outlet ofthe adsorber 3 is connected to the inlet of the adsorber 2, and inparticular via a line section 16. The now again opened outlet of theadsorber 2 is connected via a line section 17 with the drain line 5 forpurified water. At the appropriate time, the now upstream adsorber 3 isbackwashed in the same manner as was described in connection with thebiofilter 1.

On days that are free of the withdrawal of water (e.g. weekends andholidays) no purified water is needed. One separates the outlet from thebiofilter 1 from the drain line 5 for purified water, and connects it toa removal line 18. At the same time, the throughput of the biofilter 1is reduced, preferably to approximately one third of the normaloperating throughput.

For the emergency situation where both of the adsorbers 2 and 3 aredisrupted, a bypass line 20 is provided that connects the outlet of thebiofilter 1 directly to the drain line 5 for purified water.

The method of the invention is preferably operated with a constantthroughput capacity. This leads to optimal contact times and to adefined mass transfer. It was discovered that a reduction of the TOCvalue to approximately 500 ppb could be achieved. This is an averagevalue that is subjected to only slight fluctuations. The invention thusenables very long service lives in combination with a very high TOCreduction.

Various modification possibilities are within the scope of theinvention. For example, the separate removal line 18 for the biofilter 1can be eliminated if a possibility is provided for connecting the outletof the biofilter 1 to the drain line 8 for backwash water. Furthermore,one can dispense with the use of backwash air if no loosening of theactivated carbon is desired. Alternatively, the possibility exists forcarrying out the backwashing with only air. The synchronization of theupstream adsorber with the backwashing of the biofilter can be a fixedcoupling determined by a time interval. It is then possible to dispensewith the TOC measurement locations 106 and 206 as well as with thepressure differential devices 114 and 214. The operation is moreflexible if merely the sequence of the backwashing processes ismaintained. The exchange of the activated carbon of the two adsorberscan be integrated into the backwash cycles. It is not necessary toexchange the activated carbon of the biofilter.

As a modification of the described unit, it is possible to carry out thebackwashing of the biofilter and/or of the upstream adsorber only as afunction of the running time or only as a function of the build up ofthe respective pressure drop. However, the TOC measurement has proven tobe a very reliable control. The mechanical cleaning of the adsorbers is,as mentioned, preferably carried out first with air and subsequentlywith water. A purely air or water backwashing is, as also alreadymentioned, likewise possible.

The specification incorporates by reference the disclosure of Germanpriority document 199 62 791.6 filed Dec. 23, 1999 and Internationalpriority document PCT/EP00/12733 filed Dec. 14 2000.

The present invention is, of course, in no way restricted to thespecific disclosure of the specification and drawings, but alsoencompasses any modifications within the scope of the appended claims.

1. A method of purifying untreated water that is polluted withsubstances that can be biologically and adsorptively removed, whereinpurification is carried out in three stages, and said method includesthe steps of: operating an upstream purification stage as a biofilter,while subsequent downstream purification stages are operated asadsorbers; cleaning said biofilter by backwashing, wherein backwashingperiods are initiated as a function of at least one of: TOC determinedbetween said biofilter and an upstream one of said adsorbers, a runningtime, and a pressure loss over said biofilter; and cleaning saidupstream adsorber by backwashing and then shifting this adsorber to adownstream position by alternating it with another one of saidadsorbers.
 2. A method according to claim 1, which includes the step ofsynchronizing backwashing of said biofilter with backwashing of saidupstream adsorber.
 3. A method according to claim 1, which includesinitiating backwash periods of said upstream adsorber as a function ofTOC determined between said upstream adsorber and a downstream one ofsaid adsorbers.
 4. A method according to claim 3, wherein saidinitiation of said backwash periods is additionally effected as afunction of a pressure loss determined over said upstream adsorber.
 5. Amethod according to claim 3, wherein each of said backwash periodsincludes a lowering of a water level in said biofilter or in saidupstream adsorber, and then a backwashing with at least one of air andwater.
 6. A method according to claim 1, wherein during periods of timethat are free of a removal of water, said biofilter is separated fromsaid upstream adsorber, and said adsorbers are shut off.
 7. A methodaccording to claim 6, wherein said biofilter, which is separated fromsaid upstream adsorber, is operated at a reduced throughput.
 8. A methodaccording to claim 1, wherein an initiation of backwash periods of saidupstream adsorber is effected as a function of a pressure lossdetermined over said upstream adsorber.
 9. An apparatus for purifyinguntreated water that is polluted with substances that can bebiologically and adsorptively removed, said apparatus comprising: a feedline for untreated water; a drain line for purified water; a biofilterhaving an inlet and an outlet, wherein said inlet is connected to saidfeed line; a first adsorber having an inlet and an outlet; a secondadsorber having an inlet and an outlet, wherein said inlets of saidadsorbers are connectable to said feed line and to said outlet of saidbiofilter, wherein said outlets of said adsorbers are connectable tosaid drain line, wherein said outlet of said first adsorber isconnectable to said inlet of said second adsorber, and wherein saidoutlet of said second adsorber is connectable to said inlet of saidfirst adsorber; at least one of a feed and drain line for backwashwater, and a feed line for backwash air, wherein said lines areconnectable to said biofilter and to each of said adsorbers; and acontrol device for operating valves that are associated with saidbiofilter and each of said adsorbers, wherein said control device isconnected to at least one of: a TOC measurement location associated withsaid outlet of said biofilter, a throughput measurement device, and adifferential pressure measurement device for said biofilter.
 10. Anapparatus according to claim 9, wherein the outlet of each of saidadsorbers is provided with a respective TOC measurement location that isconnected to said control device.
 11. An apparatus according to claim 9,wherein each of said adsorbers is provided with a respectivedifferential pressure measurement device that is connected to saidcontrol device.
 12. An apparatus according to claim 9, wherein saidoutlet of said biofilter is connectable to a removal line.
 13. Anapparatus according to claim 9, wherein a recirculation line is providedthat is connected to said drain line for purified water and that isconnectable to said outlets of each of said adsorbers.